Method for producing bis(fluoralkyl)phosphinic acid chlorides or fluoralkylphosphonic acid chlorides

ABSTRACT

The invention relates to a process for the preparation of bis(fluoroalkyl)phosphinyl chlorides or fluoroalkylphosphonyl dichlorides by reaction of the corresponding bis(fluoroalkyl)phosphinic acid or fluoroalkylphosphonic acid with aryltetrachlorophosphorane as chlorinating agent

The invention relates to a process for the preparation of bis(fluoroalkyl)phosphinyl chlorides or fluoroalkylphosphonyl dichlorides by reaction of the corresponding bis(fluoroalkyl)phosphinic acid or fluoroalkylphosphonic acid with aryltetrachlorophosphorane as chlorinating agent.

Processes for the synthesis of phosphinyl chlorides and phosphonyl dichlorides by reaction of phosphinic acids or phosphonic acids with the chlorinating agents PCl₅ or SOCl₂ are known, for example, from L. D. Quin, “A Guide to organophosphorus Chemistry”, Wiley-Interscience, N.Y., 2000 or D. E. C. Corbridge, “Phosphorus An Outline of its Chemistry, Biochemistry and Technology (Second Edition)”, Elsevier, Amsterdam-Oxford-N.Y., 1980. These methods have preferably been used for the synthesis of non-fluorinated phosphinyl chlorides and non-fluorinated phosphonyl dichlorides.

L. M. Yagupolskii, N. V. Pavlenko, N. V. Ignat'ev, G. I. Matuschecheva, V. Ya. Semenii, Zh. Obsh. Khim. (Russ.), 54 (1984), 2, 334-339, describe a chlorination of a bis(perfluoroalkyl)phosphinic acid using PCl₅, but the bis(perfluoroalkyl)phosphinyl chloride and POCl₃ obtained have similar boiling points and work-up is therefore complex.

As an alternative, bis(perfluoroalkyl)phosphinyl chlorides can also be synthesised by oxidation of bis(perfluoroalkyl)chlorophosphines using NO₂, as known, for example, from J. E. Griffith, Spectrochim. Acta, Part A, 24A (1968), 303 or T. Mahmood, J. M. Shreeve, Inorg. Chem., 25 (1986), 3128-3131.

Bis(fluoroalkyl)phosphinyl chlorides and fluoroalkylphosphonyl dichlorides are interesting precursors for the synthesis of novel materials, for example ionic liquids. It is therefore desirable to have a synthesis of these compounds available which can be implemented economically and on a large industrial scale in order that these precursors can be prepared in large quantities.

The object of the invention is therefore to develop an improved process for the preparation of bis(fluoroalkyl)phosphinyl chlorides or fluoroalkylphosphonyl dichlorides which meets these requirements.

Surprisingly, it has been found that the use of aryltetrachlorophosphorane as chlorinating agent for the reaction with bis(fluoroalkyl)phosphinic acid or fluoroalkylphosphonic acid achieves this object.

The invention therefore relates to a process for the preparation of bis(fluoroalkyl)phosphinyl chlorides or fluoroalkyiphosphonyl dichlorides by reaction of the corresponding bis(fluoroalkyl)phosphinic acid or fluoroalkylphosphonic acid with an aryltetrachlorophosphorane as chlorinating agent.

The starting compounds bis(fluoroalkyl)phosphinic acid and fluoroalkylphosphonic acid are readily accessible starting from the commercially available tris(fluoroalkyl)difluorophosphoranes, as described, for example, in WO 03/087110 and WO 03/087111.

Of the aryltetrachlorophosphoranes, ArPCl₄, phenyltetrachiorophosphorane, for example, is a known reagent which can be prepared starting from commercially available dichlorophenylphosphine (PhPCl₂) by reaction with chlorine (A. Michaelis, Justus Liebigs Ann. Chem., 181 (1876), 322).

The abbreviation Ar in the formula ArPCl₄ stands, for example, for substituted or unsubstituted phenyl, naphthyl or anthryl. Ar particularly preferably stands for unsubstituted or substituted phenyl.

Substituted phenyl denotes phenyl which is substituted by C₁- to C₁₂-alkyl, partially fluorinated or perfluorinated C₁- to C₆-alkyl or C₃- to C₇-cycloalkyl, NO₂, F, Cl, Br, unfluorinated, partially fluorinated or perfluorinated C₁-C₆-alkoxy or PCl₄, for example o-, m- or p-methylphenyl, o-, m- or p-ethylphenyl, o-, m- or p-propylphenyl, o-, m- or p-isopropylphenyl, o-, m- or p-isobutylphenyl, m- or p-tert-butylphenyl, m- or p-nitrophenyl, p-methoxyphenyl, p-ethoxyphenyl, m- or p-(trifluoromethyl)phenyl, m- or p-(trifluoromethoxy)phenyl, o-, m- or p-fluorophenyl, o-, m- or p-chlorophenyl, o-, m- or p-bromophenyl, further preferably 2,3-, 2,4-, 2,5-, 2,6-, 3,4- or 3,5-dimethylphenyl, 2,3-, 2,4-, 2,5-, 2,6-, 3,4- or 3,5-difluorophenyl, 2,3-, 2,4-, 2,5-, 2,6-, 3,4- or 3,5-dichlorophenyl, 2,3-, 2,4-, 2,5-, 2,6-, 3,4- or 3,5-dibromophenyl, 2,3-, 2,4-, 2,5-, 2,6-, 3,4- or 3,5-dimethoxyphenyl, 5-fluoro-2-methylphenyl, 3,4,5-trimethoxyphenyl, 2,4,5-trirnethylphenyl or 2,4,6-trimethylphenyl. Ar is very particularly preferably unsubstituted phenyl.

The aryltetrachlorophosphorane is preferably selected from phenyltetrachlorophosphorane, tolyltetrachlorophosphorane and p-chlorophenyltetrachlorophosphorane. In particular, phenyltetrachlorophosphorane is used.

Straight-chain or branched alkyl groups having 1 to 6 C atoms are, for example, methyl, ethyl, isopropyl, propyl, butyl, sec-butyl or tert-butyl, pentyl, 1-, 2- or 3-methylbutyl, 1,1-, 1,2- or 2,2-dimethylpropyl, 1-ethylpropyl or hexyl or, for straight-chain or branched alkyl groups having 1 to 12 C atoms, extended, for example, by octyl or dodecyl.

Unfluorinated C₁-C₆-alkoxy corresponds to an alkoxy group of the formula OC_(p)H_(2p+1), where p=1, 2, 3, 4, 5 or 6, for example methoxy, ethoxy, propoxy, butoxy, pentoxy or hexoxy, where the alkyl groups of the alkoxy groups may be straight-chain or branched. In the case of perfluorinated alkoxy groups, all H atoms of the above-mentioned formula are replaced correspondingly by F. In the case of alkoxy groups which are partially substituted by F, only some H are replaced by F.

Unsubstituted saturated or partially or fully unsaturated cycloalkyl groups having 3-7 C atoms are therefore cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl or phenyl, which may be substituted by C₁- to C₆-alkyl groups or PCl₄.

The reaction can be carried out in an organic solvent, for example in chloroform, dichloromethane or 1,6-dibromohexane, but where the reaction can also be carried out without a solvent. The reaction is particularly preferably carried out without a solvent.

The organic solvent is preferably in dried form.

The reaction is generally carried out with equimolar amounts, i.e. 1 mol of bis(perfluoroalkyl)phosphinic acid and 1 mol of aryltetrachlorophosphorane or 1 mol of fluoroalkylphosphonic acid and 2 mol of aryltetrachlorophosphorane. However, it is also possible to use up to a two-fold excess of aryltetrachlorophosphorane. An excess of 10%, as documented in the examples, is preferably used.

The reaction can be carried out at temperatures of −20° to 200° C., preferably at temperatures of 0° to 150° C. The reaction is particularly preferably carried out at a temperature of 0° C. to room temperature for the synthesis of the bis(fluoroalkyl)phosphinyl chloride. The reaction is particularly preferably carried out at temperatures of room temperature to 80° C. for the synthesis of the fluoroalkylphosphonyl dichloride.

It may furthermore be advantageous to carry out the reaction under inert-gas conditions.

A suitable starting material for the process according to the invention for the preparation of bis(fluoroalkyl)phosphinyl chlorides is, in particular, a compound of the formula I

R¹R²P(═O)OH  I,

where

-   -   R¹ and R² each stand, independently of one another, for         straight-chain or branched alkyl groups C_(n)F_(2n+1-y)Hy, where     -   n denotes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 and y denotes         0, 1, 2, 3, 4 or 5, but where y denotes 0, 1 or 2 for n=1 or 2.

This results in bis(fluoroalkyl)phosphinyl chlorides of the formula Ia

R¹R²P(═O)Cl  Ia,

where

-   -   R¹ and R² each stand, independently of one another, for         straight-chain or branched alkyl groups C_(n)F_(2n+1-y)H_(y),         where     -   n denotes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 and y denotes         0, 1, 2, 3, 4 or 5, but where y denotes 0, 1 or 2 for n=1 or 2.

The substituents R¹ and R² may be identical or different. The two substituents R¹ and R² are particularly preferably identical.

In a particular embodiment, the substituents R¹ and R² in formula I or Ia are perfluorinated, i.e. R¹ and R² each stand, independently of one another, for a straight-chain or branched fluorinated alkyl group C_(n)F_(2n+1), where n=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12.

R¹ and R² in formula I or Ia preferably each stand, independently of one another, for trifluoromethyl, pentafluoroethyl, heptafluoropropyl or linear or branched nonafluorobutyl, very particularly preferably for pentafluoroethyl or linear nonafluorobutyl.

Furthermore, suitable starting materials for the process according to the invention for the preparation of bis(fluoroalkyl)phosphinyl chlorides of the formula Ia are also the salts of the acid R¹R²P(═O)OH of the formula I, i.e. salts of the formula [R¹R²P(═O)O⁻]Kt^(m+), where Kt^(m+) is an inorganic cation, preferably Na⁺, K⁺, Ca²⁺, Mg²⁺, Zn²⁺, or an organic cation, preferably ammonium or phosphonium, and m=1 or 2.

Preferred ammonium cations are [NH₄]⁺ or tetraalkylammonium cations, where the alkyl groups can have 1 to 6 C atoms and may be straight-chain or branched. The alkyl groups are preferably identical.

Preferred phosphonium cations are tetraalkylphosphonium cations, where the alkyl groups can have 1 to 6 C atoms and may be straight-chain or branched, tetraatylphosphonium cations, where “aryl” corresponds to one of the above-mentioned meanings for Ar, or triarylalkylphosphonium cations, where “aryl” corresponds to one of the above-mentioned meanings and “alkyl” denotes an alkyl group having 1 to 6 C atoms, which may be straight-chain or branched. The alkyl groups or aryl groups in the tetraalkylphosphonium cations or tetraarylphosphonium cations are preferably identical. The aryl groups in trisarylalkylphosphonium cations are preferably identical.

A suitable starting material for the process according to the invention for the preparation of fluoroalkylphosphonyl dichlorides is, in particular, a compound of the formula II

R¹P(═O)(OH)₂  II,

where

-   -   R¹ stands for a straight-chain or branched alkyl group         C_(n)F_(2n+1-y)H_(y), where n denotes 1, 2, 3, 4, 5, 6, 7, 8, 9,         10, 11 or 12 and y denotes 0, 1, 2, 3, 4 or 5, but where y         denotes 0, 1 or 2 for n=1 or 2.

This results in fluoroalkylphosphonyl dichlorides of the formula IIa

R¹P(═O)(Cl)₂  IIa,

where

-   -   R¹ stands for a straight-chain or branched alkyl group         C_(n)F_(2n+1-y)H_(y), where n denotes 1, 2, 3, 4, 5, 6, 7, 8, 9,         10, 11 or 12 and y denotes 0, 1, 2, 3, 4 or 5, but where y         denotes 0, 1 or 2 for n=1 or 2.

In a particular embodiment, the substituent R¹ of the formula II or IIa is perfluorinated, i.e. R¹ in each case stands, independently of one another, for a straight-chain or branched fluorinated alkyl group C_(n)F_(2n+1), where n=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12.

R¹ in formula II or IIa preferably stands for trifluoromethyl, pentafluoroethyl, heptafluoropropyl or linear or branched nonafluorobutyl, very particularly preferably for pentafluoroethyl or linear nonafluorobutyl.

Furthermore, suitable starting materials for the process according to the invention for the preparation of fluoroalkylphosphonyl dichlorides of the formula IIa are also the salts of the acid R¹P(═O)(OH)₂ of the formula II, i.e. salts of the formula [R¹P(═O)O₂]²⁻ m Kt⁺, where Kt⁺ is an inorganic cation, preferably Na⁺, K⁺, Ca²⁺, Mg²⁺, Zn²⁺, or an organic cation, preferably ammonium or phosphonium, and m=1 or 2, depending on the charge of the cation used.

Preferred ammonium cations are [NH₄]⁺ or tetraalkylammonium cations, where the alkyl groups can have 1 to 6 C atoms and may be straight-chain or branched. The alkyl groups are preferably identical.

Preferred phosphonium cations are tetraalkylphosphonium cations, where the alkyl groups can have 1 to 6 C atoms and may be straight-chain or branched, tetraarylphosphonium cations, where “aryl” corresponds to one of the above-mentioned meanings for Ar, or triarylalkylphosphonium cations, where “aryl” corresponds to one of the above-mentioned meanings and “alkyl” denotes an alkyl group having 1 to 6 C atoms, which may be straight-chain or branched. The alkyl groups or aryl groups in the tetraalkylphosphonium cations or tetraarylphosphonium cations are preferably identical. The aryl groups in trisarylalkyiphosphonium cations are preferably identical.

The process according to the invention enables a synthesis of bis(fluoroalkyl)phosphinyl chlorides or fluoroalkylphosphonyl dichlorides in a yield which is improved compared with the prior art. Furthermore, this process is suitable for a large-scale industrial synthesis, since the purification and separation of by-products, caused by the aryitetrachlorophosphorane, is simplified and only low equipment complexity is necessary in this respect. The by-product C₆H₅P(O)Cl₂ has, for example, a boiling point of 258° C. at atmospheric pressure according to the literature (Gutmann et al., Monatsh. Chem., 91, 1960, pp. 836-839). This boiling point differs significantly from that of the product, meaning that separation of the by-product is simplified.

Even without further comments, it is assumed that a person skilled in the art will be able to utilise the above description in the broadest scope. Thus, the process according to the invention also facilitates, for example, the preparation of perfluoroalkylcarbonyl chlorides from periluoroalkylcarboxylic acids having 2 to 12 C atoms, preferably having 2 to 8 C atoms, or from salts thereof by reaction with aryltetrachlorophosphorane.

The process according to the invention also facilitates, for example, the preparation of perfluorinated dicarboxylic acid dichlorides from dicarboxylic acids having 3 to 10 C atoms, preferably having 4 to 8 C atoms, or from salts thereof by reaction with aryltetrachlorophosphorane.

The preferred embodiments and examples should therefore merely be regarded as descriptive disclosure which is absolutely not limiting in any way.

EXAMPLES

The NMR spectra were measured on solutions in deuterated solvents at 20° C. in a Bruker Avance 300 spectrometer with a 5 mm ¹H/BB broadband probe with deuterium lock, unless indicated in the examples. The measurement frequencies of the various nuclei are: ¹H: 300.13 MHz, ¹⁹F: 282.41 MHz and ³¹P: 121.49 MHz. The referencing method is indicated separately for each spectrum or each data set.

Example 1 a) Synthesis of Phenyltetrachlorophosphorane, PhPCl₄

C₆H₅PCl₂+Cl₂→C₆H₅PCl₄

30.1 g (0.168 mol) of dichlorophenylphosphine in 130 ml of dry chloroform are initially introduced, and 11.9 g (0.168 mol) of chlorine gas are passed in for about 20 minutes, during which the temperature is held at 30° C. The solvent is then removed, giving 40.7 g of a solid, identified as phenyltetrachlorophosphorane.

Melting point: 73-74° C. (lit., 73° C.: J. Lindner, W. Wirth, B. Zaunbauer, Monatsh. Chem., 70 (1937), 1-19).

³¹P NMR (CDCl₃; standard: 85% H₃PO₄), δ, ppm: −42.6 m.

b) Synthesis of Bis(pentafluoroethyl)phosphinyl Chloride

(C₂F₅)₂P(O)OH+C₆H₅PCl₄→(C₂F₅)₂P(O)Cl+HCl+C₆H₅P(O)Cl₂

21.75 g (72 mmol) of bis(pentafluoroethyl)phosphinic acid are added dropwise at room temperature to 20.0 g (80 mmol) of phenyltetrachlorophosphorane, and the mixture is stirred for four hours. Bis(pentafluoroethyl)phosphinyl chloride is separated off by distillation at atmospheric pressure, giving 18.1 g of bis(pentafluoroethyl)phosphinyl chloride, which corresponds to a yield of 78%, based on the phosphinic acid employed.

Boiling point: 86-88° C.

¹⁹F NMR (pure substance; CD₃CN film; standard: CCl₃F), δ, ppm: −82:0 s (2CF₃), −120.1 d,d (2F_(A)), −124.4 d,d (2F_(B)), ²J_(P,F(A))=92 Hz, ²J_(P,F(B))=100 Hz, ²J_(F(A),F(B))=323 Hz.

³¹P NMR (pure substance; CD₃CN film; standard: 85% H₃PO₄), δ, ppm: 20.8 t,t.

Example 2 Synthesis of Bis(nonafluorobutyl)phosphinyl Chloride

(C₄F₉)₂P(O)OH+C₆H₅PCl₄→(C₄F₉)₂P(O)Cl+HCl+C₆H₅P(O)Cl₂

Variant a) 2.49 g (5.0 mmol) of bis(nonafluorobutyl)phosphinic acid are added dropwise at room temperature to a solution of 1.47 g (5.9 mmol) of phenyltetrachlorophosphorane in 3 cm³ of dry chloroform, and the mixture is stirred for a further 50 minutes. Chloroform is separated off by distillation, and bis(nonafluorobutyl)phosphinyl chloride is distilled off at atmospheric pressure, giving 1.62 g of bis(nonafluorobutyl)phosphinyl chloride, which corresponds to a yield of 63%, based on the phosphinic acid employed.

Variant b) The mixture of 4.6 g (18.4 mmol) of phenyltetrachlorophosphorane and 7.3 g (14.5 mmol) of bis(nonafluorobutyl)phosphinic acid is stirred at room temperature for four hours When the evolution of gas (HCl) is complete, the nonafluorobutylphosphonyl dichloride is separated off by distillation at atmospheric pressure, giving 5.73 g of bis(nonafluorobutyl)phosphinyl chloride as colourless liquid substance. This corresponds to a yield of 76%, based on the phosphinic acid employed.

Boiling point: 158-160° C.

¹⁹F NMR (pure substance; CD₃CN film; standard: CCl₃F), δ, ppm: −84.3 t,m (2CF₃), −115.4 d,d (2F_(A)), −119.7 d,d (2F_(B)), −121.5 m (2CF₂), −128.6 m (2CF₂), ²J_(P,F(A))=95 Hz ²J_(P,F(B))=102 Hz, ²J_(F(A),F(B))=328 Hz, ⁴J_(F,F)=10 Hz, ⁴J_(F,F)=14 Hz.

³¹P NMR (pure substance; CD₃CN film; standard: 85% H₃PO₄), δ, ppm: 21.8 t,t.

Example 3 Synthesis of Pentafluoroethylphosphonyl Dichloride

(C₂F₅)P(O)(OH)₂+2C₆H₅PCl₄→(C₂F₅)P(O)Cl₂+2HCl+2C₆H₅P(O)Cl₂

6.46 g (32 mmol) of pentafluoroethylphosphonic acid are added dropwise at 0° C. (ice bath) to 19.0.g (76 mmol) of phenyltetrachlorophosphorane with vigorous mixing. The reaction mixture is then stirred at room temperature for four hours. Pentafluoroethylphosphonyl dichloride is separated off by distillation at atmospheric pressure, giving 4.64 g of pentafluoroethylphosphonyl dichloride as colourless liquid substance, which corresponds to a yield of 61%, based on the phosphonic acid employed.

Boiling point: 77-79° C.

¹⁹F NMR (pure substance; CD₃CN film; standard: CCl₃F), δ, ppm: −80.9 s (CF₃); −122.5 d (CF₂), ²J_(P,F)=110 Hz.

³¹P NMR (pure substance; CD₃CN film; standard: 85% H₃PO₄), δ, ppm: 17.7 t.

Example 4 Synthesis of Nonafluorobutylphosphonyl Dichloride

(C₄F₉)P(O)(OH)₂+2C₆H₅PCl₄→(C₄F₉)P(O)Cl₂+2HCl+2C₆H₅P(O)Cl₂

The mixture of 11.0 g (44 mmol) of phenyltetrachlorophosphorane and 5.5 g (18.3 mmol) of nonafluorobutylphosphonic acid is stirred at 40° C. (bath temperature) for two hours. Nonafluorobutylphosphonyl dichloride is separated off by distillation at atmospheric, pressure, giving 3.77 g of nonafluorobutylphosphonyl dichloride as colourless liquid substance, which corresponds to a yield of 61%, based on the phosphonic acid employed.

Boiling point: 124-126° C.

¹⁹F NMR (pure substance, CD₃CN film; standard: CCl₃F), δ, ppm: −83.8 t,m (CF₃), −118.5 d (CF₂), −121.4 m (CF₂), −128.4 m (CF₂), ²J_(P,F)=113 Hz, ⁴J_(F,F)=10 Hz, ⁴J_(F,F)=14 Hz.

³¹P NMR (pure substance, CD₃CN film; standard: 85% H₃PO₄), δ, ppm: 17.8 t. 

1. Process for the preparation of bis(fluoroalkyl)phosphinyl chlorides or fluoroalkylphosphonyl dichlorides by reaction of the corresponding bis(fluoroalkyl)phosphinic acid or fluoroalkylphosphonic acid with aryltetrachlorophosphorane as chlorinating agent.
 2. Process according to claim 1, characterised in that the bis(fluoroalkyl)phosphinic acid employed is a compound of the formula I R¹R²P(═O)OH  I, where R¹ and R² each stand, independently of one another, for straight-chain or branched alkyl groups C_(n)F_(2n+1-y)H_(y), where n denotes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 and y denotes 0, 1, 2, 3, 4 or 5, but where y denotes 0, 1 or 2 for n=1 or
 2. 3. Process according to claim 1, characterised in that the fluoroalkylphosphonic acid employed is a compound of the formula II R¹P(═O)(OH)₂  II, where R¹ stands for a straight-chain or branched alkyl group C_(n)F_(2n+1-y)H_(y), where n denotes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 and y denotes 0, 1, 2, 3, 4 or 5, but where y denotes 0, 1 or 2 for n=1 or
 2. 4. Process according to claim 1, characterised in that the aryltetrachlorophosphorane employed is phenyltetraehlorophosphorane.
 5. Process according to claim 1, characterised in that the reaction is carried out at temperatures between 20° C. and 200° C. 